In rapid fire large caliber automatic weapons systems in general the firing chambers are fixed stationarily with respect to the receiver. The lock mechanism for locking the cartridge in the firing chamber has been categorized as either sliding lock mechanisms or rotating lock mechanisms. Sliding lock and rotating lock mechanisms have required considerable energy expenditure for movement thereof. In the sliding lock case, friction contributed to the energy requirements, and, in the rotating lock case, the size of the lock, not only presented energy and inertia problems, but also increased the receiver size requirements.
Another problem common to these two locking mechanisms was that the head space tolerances of the firing chamber imposed additional requirements in the design of the lock mechanisms.
The foregoing problems also existed with weapon systems of the reciprocating firing chamber type as well as problems of locking and unlocking timing functions coordinated to the firing cycle of the weapon.
Reciprocating firing chambers, in addition to the locking problems, also presented problems of synchronization of the movement of the firing chamber between the in and out of battery positions with the firing cycle demands of the weapon system.